They might use your Google Pay to see if you have a credit card attached and use that to confirm you are over 18. This is one of the age verification methods YT does.
I noticed recently I couldn't use my 2FA key to get in to Google, but I never got a notification about it. Don't know when it was removed or why but was annoying getting back in (especially as text verification was a disabled option for some reason), and then setting it back up again.